Bisamineazaallylic ligands and their use in atomic layer deposition methods

ABSTRACT

Methods for deposition of elemental metal films on surfaces using metal coordination complexes comprising bisamineazaallylic ligands are provided. Also provided are bisamineazaallylic ligands useful in the methods of the invention and metal coordination complexes comprising these ligands.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional under 35 U.S.C. §121 of U.S.application Ser. No. 13/189,644, filed Jul. 25, 2011, which claimspriority to U.S. Provisional Application Ser. No. 61/407,970, filed Oct.29, 2010 the disclosures of which are hereby incorporated by referencein their entirety.

TECHNICAL FIELD

The present invention relates generally to methods of depositing thinfilms of elemental metal and to metal coordination complexes useful insuch methods. In particular, the invention relates to coordinationcomplexes of metal cations with multidentate azaallylic ligands andtheir use in atomic layer deposition processes.

BACKGROUND

Deposition of thin films on a substrate surface is an important processin a variety of industries including semiconductor processing, diffusionbarrier coatings and dielectrics for magnetic read/write heads. In thesemiconductor industry, in particular, miniaturization requires atomiclevel control of thin film deposition to produce conformal coatings onhigh aspect structures. One method for deposition of thin films withatomic layer control and conformal deposition is atomic layer deposition(ALD), which employs sequential, self-limiting surface reactions to formlayers of precise thickness controlled at the Ångstrom or monolayerlevel. Most ALD processes are based on binary reaction sequences whichdeposit a binary compound film. Each of the two surface reactions occurssequentially and because they are self-limiting a thin film can bedeposited with atomic level control. Because the surface reactions aresequential, the two gas phase reactants are not in contact and possiblegas phase reactions that may form and deposit particles are limited. Theself-limiting nature of the surface reactions also allows the reactionto be driven to completion during every reaction cycle, resulting infilms that are continuous and pinhole-free.

ALD has been used to deposit metals and metal compounds on substratesurfaces. Al₂O₃ deposition is an example of a typical ALD processillustrating the sequential and self-limiting reactions characteristicof ALD. Al₂O₃ ALD conventionally uses trimethylaluminum (TMA, oftenreferred to as reaction “A” or the “A” precursor) and H₂O (oftenreferred to as the “B” reaction or the “B” precursor). In step A of thebinary reaction, hydroxyl surface species react with vapor phase TMA toproduce surface-bound AlOAl(CH₃)₂ and CH₄ in the gas phase. Thisreaction is self-limited by the number of reactive sites on the surface.In step B of the binary reaction, AlCH₃ of the surface-bound compoundreacts with vapor phase H₂O to produce AlOH bound to the surface and CH₄in the gas phase. This reaction is self-limited by the finite number ofavailable reactive sites on surface-bound AlOAl(CH₃)₂. Subsequent cyclesof A and B, purging gas phase reaction products and unreacted vaporphase precursors between reactions and between reaction cycles, producesAl₂O₃ growth in an essentially linear fashion to obtain the desired filmthickness.

While perfectly saturated monolayers are desired, this goal is verydifficult to achieve in practice. The typical approach to further ALDdevelopment has been to determine whether or not currently availablechemistries are suitable for ALD. Chemistries which have been exploredfor use in ALD processes include metal halides, metal alkyls, metalalkoxides, beta-diketonates, amides, imido/amido complexes amidinates,cyclopentadienyl complexes and mixed systems of the foregoing compounds.In addition, prior art processes for ALD have been most effective fordeposition of metal oxide and metal nitride films. Although a fewprocesses have been developed that are effective for deposition ofelemental ruthenium and other late transition metals, in general ALDprocesses for deposition of pure metal have not been sufficientlysuccessful to be adopted commercially. There is a need for newdeposition chemistries that are commercially viable, particularly in thearea of elemental metal films. The present invention addresses thisproblem by providing novel chemistries which are specifically designedand optimized to take advantage of the atomic layer deposition process.

SUMMARY

In one embodiment, the present invention provides methods for producingthin films of elemental metal on a substrate using metal coordinationcomplexes as source material, wherein at least one coordinating ligandis a bisamineazaallylic compound. The thin films may be produced usingatomic layer deposition (ALD) processes, including plasma enhancedatomic layer deposition (PEALD) processes. In addition, plasma andthermal ALD processes are both applicable to the methods of theinvention.

In an alternative embodiment, the method for producing elemental metalthin films using metal coordination complexes including at least onebisamineazaallylic ligand is a chemical vapor deposition (CVD) process.

In a further embodiment, the metal coordination complexes used in themethods of the invention comprise at least one multidentatebisamineazaallylic ligand. In a specific embodiment thebisamineazaallylic ligand is tridentate. The ligand may be any L asdefined below. However, in a further specific embodiment the metalcation of the coordination complex is coordinated with two tridentatebisamineazaallylic ligands, which may be the same (homoleptic) ordifferent (heteroleptic). A specific example of one of the metalcomplexes formed by coordination with two tridentate bisaminoazaalyllicligands may be represented by formula (III):

wherein M is a transition metal and each R is independently H, halide,linear or branched C₁₋₆ alkyl, acyl, aldehyde, keto, C₂ alkenyl, or isabsent thereby forming an adjacent double bond; or one or more of R₂ andR₃, R₆ and R₇, R₁₀ and R₁₁ or R₁₄ and R₁₅ together with the nitrogenatom to which they are attached form an optionally substituted aromaticor alicyclic ring. The optionally substituted aromatic or alicyclic ringmay consist of three, four or five ring carbon atoms.

In a further specific embodiment, at least one tridentatebisamineazaallylic ligand forms two dative M-N bonds (wherein M is themetal cation) and one azaallyl coordination bond with the metal cation.In a further specific embodiment, two tridentate bisamineazaallylicligands each form two dative M-N bonds (wherein M is the metal cation)and one azaallyl coordination bond with the metal cation. An example ofthis type of metal coordination complex is represented by formula (IV):

which is commonly referred to as a bis(bispyridinylazaallylic) metalcoordination complex.

In an alternative embodiment, the metal coordination complexes useful inthe methods of the invention comprise a single tridentatebisamineazaallylic ligand coordinated with the metal cation and themetal cation is additionally coordinated to at least one neutral oranionic ligand such as halogen (such as Cl), alkyl (such as C₁₋₃ alkyl),amido and imido; or to at least one mixed ligand other than an NNNligand, such as amidinate, amido-amino and pyrollyl-amino.

In another embodiment, the invention provides a method for synthesizingbisamineazaallylic ligands used in the methods of the invention, whereinthe synthesis method comprises reacting an aldehyde compound representedby formula R₁R₂N—CH₂—COH with a compound represented by formula:R₃R₄N—CH₂—CH₂NH₂ to form a reaction product represented by formulaR₁R₂N—CH₂—CH═N—CH₂—CH₂—NR₃R₄. The reaction product is treated withlithium hexamethyldisilazide (LHMDS) to produce the ligand coordinatedwith a lithium ion. The ligand may then be complexed with the desiredtransitional metal cation by reaction with the desired transition metalhalide.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE illustrates an exemplary ALD process according to theinvention.

DETAILED DESCRIPTION

Before describing several exemplary embodiments of the invention, it isto be understood that the invention is not limited to the details ofconstruction or process steps set forth in the following description.The invention is capable of other embodiments and of being practiced orbeing carried out in various ways. It is also to be understood that thecomplexes and ligands of the present invention may be illustrated hereinusing structural formulas which have a particular stereochemistry. Theseillustrations are intended as examples only and are not to be construedas limiting the disclosed structure to any particular stereochemistry.Rather, the illustrated structures are intended to encompass all suchcomplexes and ligands having the indicated chemical formula.

Reference throughout this specification to “one embodiment,” “certainembodiments,” “one or more embodiments” or “an embodiment” means that aparticular feature, structure, material, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe invention. Thus, the appearances of the phrases such as “in one ormore embodiments,” “in certain embodiments,” “in one embodiment” or “inan embodiment” in various places throughout this specification are notnecessarily referring to the same embodiment of the invention.Furthermore, the particular features, structures, materials, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

L, as used in the formulas disclosed herein, represents a ligandselected from the group consisting of neutral ligands (L_(neutral)),anionic ligands (L_(anionic)) and mixed ligands (L_(mixed)). Examples ofneutral ligand molecules include no ligand, carbonyl, amino,bis-(pyridyl) and diamine; examples of anionic ligands include halogen(such as Cl), alkyl (such as C₁₋₃ alkyl), amido and imido; and examplesof mixed ligands include the NNN ligands of the type disclosed herein,amidinate, amido-amino and pyrolly-amino. As is understood in the art, Lmay be any combination of L_(neutral), L_(anionic) and L_(mixed)depending on the oxidation state of M. When “L” is used withoutindication of its charge it is intended to refer generically to all suchligand types.

The term “metal coordination complex” as used herein includes metalchelate complexes wherein a metal ion is coordinated with one or morepolydentate ligands and metal coordination complexes wherein a metal ionis coordinated with one or more monodentate ligands. As will bediscussed in more detail below, the metal complexes of the invention mayconsist only of chelating ligands or they may comprise both chelatingligands and coordinating ligands. The term “metal coordination complex”refers to both types of metal complex. The chelate effect of thepolydentate ligand provides enhanced affinity for the metal ion in thecomplex as compared to the affinity of any nonchelating (monodentate)ligands in the complex for the same metal ion.

In general, ligands useful in the elemental metal thin layer depositionmethods of the invention include multidentate (chelating) ligands whichform at least one bond of covalent character to the metal center and atleast one weaker bond to the metal center which involves dative bondingfrom the ligand. While not intending to be bound by theory, it isbelieved that the chelate effect helps to stabilize the metal-ligandprecursor complex in the vapor phase while maintaining the ability toprovide an active site for nucleation of the precursor on a surface.

An ALD process is used in one embodiment of the method of the inventionfor preparing thin films of elemental metal. In this aspect of theinvention the metal coordination complex used in the ALD process isrepresented by formula (I), which may be referred to herein as anL-(bisamineazaallylic) metal coordination complex:

wherein M is a transition metal and each R is independently H, halide,linear or branched C₁₋₆ alkyl, acyl, aldehyde, keto, C₂₋₄ alkenyl, or isabsent thereby forming an adjacent double bond; or one or more of R₂ andR₃ or R₆ and R₇ together with the nitrogen atom to which they areattached form an optionally substituted aromatic or alicyclic ring. Theoptionally substituted aromatic or alicyclic ring may consist of three,four or five ring carbon atoms. L is an M-coordinating ligand as definedabove.

An example of a suitable NNN ligand is represented by formula (II):

each R is independently H, halide, linear or branched C₁₋₆ alkyl, acyl,aldehyde, keto, C₂₋₄ alkenyl, or is absent thereby forming an adjacentdouble bond; or one or more of R₁₀ and R₁₁ or R₁₄ and R₁₅ together withthe nitrogen atom to which they are attached form an optionallysubstituted aromatic or alicyclic ring. The optionally substitutedaromatic or alicyclic ring may consist of three, four or five ringcarbon atoms. It will be recognized that the carbon atom at eitherR₁₀/R_(10a) or R₁₄/R_(14a), or both, can form a double bond with theadjacent nitrogen in the NNN ligands described herein, and that wheneither of these carbons forms such a double bond one of R₁₀ and R_(10a)or one of R₁₄ and R_(14a) will be absent. The ligand represented byformula (II) may be referred to herein as a bisamineazaallylic ligand.

The bisamineazaallylic ligand represented by formula (II) may also berepresented in its protonated form by formula (II′):

wherein each R is defined as above with respect to formula (II).

The foregoing metal coordination complex wherein L is an NNN ligand maybe represented in one aspect by formula (III), which may be referred toherein as a bis(bisamineazaallylic) metal coordination complex:

wherein each R is as defined above.

In one embodiment of the metal coordination complex represented byformula (I) for use in the invention, R₁, R₄, R₅ and R₈ areindependently H, methyl or ethyl, and; R₂ and R₃, and R₆ and R₇ togetherwith the nitrogen atoms to which they are attached independently formpyridinyl. If L is an NNN ligand represented by formula (II), in aspecific embodiment represented by formula (III) R₉, R₁₂, R₁₃ and R₁₆may also be independently H, methyl or ethyl, and; R10 and R₁₁, and R₁₄and R₁₅ together with the nitrogen atoms to which they are attached mayform pyridinyl.

In a specific embodiment of the metal coordination complex representedby formula (I) for use in the methods of the invention, R₁, R₄, R₅ andR₈, are H; and R₂ and R₃ and R₆ and R₇ together with the nitrogen atomto which they are attached form pyridinyl. If L is an NNN ligandrepresented by formula (II), in a specific embodiment represented byformula (III) R₉, R₁₂, R₁₃ and R₁₆ may also be independently H, methylor ethyl, and; R10 and R₁₁, and R₁₄ and R₁₅ together with the nitrogenatoms to which they are attached form pyridinyl.

It is to be understood that, depending on the oxidation state of M, whenL is a non-NNN ligand it may represent one or more ligands, each ofwhich may independently be neutral (L_(neutral)) or anionic(L_(anionic)). For example, L may be three L_(neutral) ligands in ametal (I) coordination complex of the invention, L may be oneL_(anionic) and two L_(neutral) ligands in a metal (II) coordinationcomplex of the invention, L may be two L_(anionic) and one L_(neutral)ligand in a metal (III) coordination complex of the invention and L maybe three L_(anionic) ligands in a metal (IV) complex of the invention.

In an embodiment of the ALD deposition methods of the invention, a metalcoordination complex represented by formula (I) is vaporized and flowedin the vapor phase to a substrate within a deposition chamber. Thesubstrate has a surface that is either activated for reaction with themetal coordination complex or appropriate for adsorption of the metalcoordination complex to the surface to form a first layer on thesubstrate. The reaction between the L-(bisamineazaallylic) metalcoordination complex and the surface may occur by an exchange reactionbetween the surface and the complex to generate H-L and a surface boundmetal species. The reaction time, temperature and pressure are selectedto create the metal-surface interaction and achieve a layer on thesurface of the substrate. The first layer comprises the metal bound tothe surface and coordinated with one azaallylic ligand, i.e., in abisamineazaallylic metal coordination complex. Following formation ofthe first monolayer, unreacted precursor gas containing theL-(bisamineazaallylic) metal coordination complex and H-L are purgedfrom the deposition chamber using an inert gas. A reducing gas is thenflowed into the deposition chamber to reduce the covalent bond betweenthe metal and the azaallylic nitrogen, releasing the second (NNN) ligandand leaving an atomic layer of elemental metal on the substrate.H-(bisamineazaallylic) ligand which is generated is then purged from thechamber.

Optionally, a second atomic layer of elemental metal may be formed onthe first atomic layer by repeating the steps of the reaction cycle.Hydrogen remaining from the preceding reduction reaction is purged fromthe deposition chamber using an inert gas and the metal coordinationcomplex represented by formula (I) in vapor phase is again flowed intothe chamber into contact with the metal film on the substrate surface.An exchange reaction may occur between the L-(bisamineazaallylic) metalcoordination complex in the vapor phase and the metal of the firstatomic layer. This generates H-L and leaves the metal atom of thebisamineazaallylic metal complex bound to the metal atom of the firstatomic layer. The reaction time, temperature and pressure are selectedto create the metal-metal interaction and produce a layer on the surfaceof the substrate. Unreacted vapor phase L-(bisamineazaallylic) metalcomplex and H-L are purged from the deposition chamber using an insertgas. A reducing gas is flowed into the deposition chamber to reduce thecovalent bond between the metal and the azaallylic nitrogen, releasingthe second ligand and producing a second atomic layer of elemental metalon the first atomic layer of elemental metal. H-(bisamineazaallylic)ligand is then purged from the chamber.

Additional repetitions of the deposition cycle may be used to build alayer of elemental metal of the desired thickness.

A specific embodiment of the method of the invention for preparing thinfilms of elemental metal is the ALD method illustrated in FIG. 1 whichuses as an example a metal coordination complex represented by formula(IV):

The coordination complex represented by formula (IV) comprises twodi-heteroaryl (pyridinyl) azaallyl ligands as disclosed by Wolczanski,et al. (US PGPub No. 2010/0204473). The surface of the substrate onwhich the metal film is to be deposited may be an activated surface,illustrated in FIG. 1 as having available hydrogen atoms. Thebis(bispyridinylazaallylic) metal complex in vapor phase, optionally ina mixture with an inert carrier gas, is flowed into a deposition chambercontaining the substrate and over the substrate surface to effect anexchange reaction wherein a hydrogen atom on the surface displaces oneof the two ligands from the metal center. This creates a metal-surfaceinteraction and releases one of the two ligands in the metalcoordination complex in reduced form. The surface may be exposed to thebis(bispyridinylazaallylic) metal coordination complex for sufficienttime to optimize adsorption on the surface, producing a layer ofbispyridinylazaallylic metal coordination complex on the surface.

Unreacted bis(bispyridinylazaallylic) metal coordination complex andreleased bispyridinylazaallylic ligand in the vapor phase are thentypically purged from the ALD system using an inert gas such as nitrogenor argon. Purging is followed by addition of a reducing agent in gaseousform, for example hydrogen gas, which is flowed over the surface so thata second exchange reaction occurs between the hydrogen atoms of the gasand the bispyridinylazaallylic metal coordination complex on thesurface. This reaction displaces the second ligand from thesurface-bound complex and reduces the atom of metal bound to the surfaceto elemental form. The second exchange reaction is allowed to proceedfor a time sufficient to exchange bispyridinylazaallylic metalcoordination complexes on the surface, resulting in an atomic layer ofelemental metal.

The ALD system is purged of released ligand and unreacted hydrogen. If asingle atomic layer of elemental metal is desired, the process iscomplete.

Optionally, additional cycles of reacting thebis(bispyridinylazaallylic) metal coordination complex with the surface,purging and reacting the bound bispyridinylazaallylic metal coordinationcomplexes with hydrogen can be performed, each producing an additionalatomic layer of elemental metal on the surface. In this way a thin filmof the desired thickness can be achieved.

In an alternative embodiment of ALD according to the invention, anL_(anionic)-bisamineazaallylic metal coordination complex or aL_(neutral)-bisamineazaallylic metal coordination complex is used as themetal source material. In this case the bond between the metal andL_(anionic) or L_(neutral) is reduced by hydrogen atoms on the substratesurface, releasing HL_(anionic) or HL_(neutral) which is purged prior tointroduction of the reducing gas. The reducing gas, such as hydrogen,reduces the covalent bond between the metal and the azaallyl nitrogen torelease the bisamineazaallylic (NNN) ligand and form the first atomiclayer of elemental metal on the surface. Repeating deposition cycles asdescribed above builds the elemental metal thin film to the desiredthickness.

In embodiments where the metal coordination complex has sufficientflexibility, disassociation of one of the dative nitrogen-metal bondsmay allow an alternative mechanism for deposition of elemental metalthin films. These complexes typically include a bisamineazaallylicligand represented by formula (V) below in which each R isindependently, H, halide, linear or branched C₁₋₆ alkyl, acyl, aldehyde,keto, C₂₋₄ alkenyl or is absent thereby forming an adjacent double bond;or only one of R₂ and R₃ or R₆ and R₇ together with the nitrogen atom towhich they are attached form an optionally substituted aromatic oralicyclic ring. In this embodiment, the pendant amine groups canstabilize the metal center but may also readily disassociate to providean active site for bonding of M with the substrate surface. Such bondingmay occur either by adsorption to a bare metal substrate surface or byreaction with an electron donating group (such as NH₂ or OH) on thesubstrate surface. Remaining coordination bonds (to L and to thebisamineazaallylic ligand) may then be reduced to release the ligandsand leave elemental M bound to the substrate surface, generally asdescribed above. Also as described above, deposition cycles may berepeated as necessary to produce an elemental metal film of the desiredthickness.

The substrate for deposition of the elemental thin layer films may beany substrate suitable for conformal film coating in an ALD or CVDprocess. Such substrates include silicon, silica or coated silicon,metals, metal oxides and metal nitrides. In one aspect of the invention,the substrate is a semiconductor substrate.

The L-bisamineazaallylic metal coordination complexes useful in themethods of the invention include as the coordinated metal M any of thetransition metals (Groups 3-12 of the periodic table of the elements) orany of the boron group metals (Group 13). Of these, copper, silver,gold, palladium, platinum, rhodium, iridium, tungsten, titanium,zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum,manganese and ruthenium are of particular interest as elemental metalthin films and may be incorporated into the L-bisamineazaallylic metalcoordination complexes of the invention as is known in the art based ontheir oxidation states.

The reaction conditions for the ALD reaction will be selected based onthe properties of the selected L-(bisamineazaallylic) metal coordinationcomplex. The deposition can be carried out at atmospheric pressure butis more commonly carried out at a reduced pressure. The vapor pressureof the L-(bisamineazaallylic) metal coordination complex should be highenough to be practical in such applications. The substrate temperatureshould be low enough to keep the bonds between the metal atoms at thesurface intact and to prevent thermal decomposition of gaseousreactants. However, the substrate temperature should also be high enoughto keep the source materials (i.e., the reactants) in the gaseous phaseand to provide sufficient activation energy for the surface reaction.The appropriate temperature depends on the specificL-(bisamineazaallylic) metal coordination complex used and the pressure.The properties of a specific L-(bisamineazaallylic) metal coordinationcomplex for use in the ALD deposition methods of the invention can beevaluated using methods known in the art, allowing selection ofappropriate temperature and pressure for the reaction. In general, lowermolecular weight and the presence of functional groups that increase therotational entropy of the ligand sphere result in a melting point thatyields liquids at typical delivery temperatures and increased vaporpressure.

An optimized L-(bisamineazaallylic) metal coordination complex for usein the deposition methods of the invention will have all of therequirements for sufficient vapor pressure, sufficient thermal stabilityat the selected substrate temperature and sufficient reactivity toproduce a self-limiting reaction on the surface of the substrate withoutunwanted impurities in the thin film or condensation. Sufficient vaporpressure ensures that molecules of the source compound are present atthe substrate surface in sufficient concentration to enable a completeself-saturating reaction. Sufficient thermal stability ensures that thesource compound will not be subject to the thermal decomposition whichproduces impurities in the thin film.

Any multidentate ligand represented by formula (V) (also referred toherein as an NNN ligand) with sufficiently high vapor pressureproperties may be used in the thin layer film deposition methods of theinvention:

wherein each R is independently, H, halide, linear or branched C₁₋₆alkyl, acyl, aldehyde, keto, C₂₋₄ alkenyl or is absent thereby formingan adjacent double bond; or one or more of R₂ and R₃ or R₆ and R₇together with the nitrogen atom to which they are attached form anoptionally substituted aromatic or alicyclic ring. The optionallysubstituted aromatic or alicyclic ring may consist of three, four orfive ring carbon atoms. It will be recognized that the carbon atom ateither R₂/R_(2a) or R₆/R_(6a), or both, can form a double bond with theadjacent nitrogen in the NNN ligands disclosed herein, and that wheneither of these carbons forms such a double bond one of R₂ and R_(2a) orone of R₆ and R_(6a) will be absent.

The bisamineazaallylic ligand represented by formula (V) may also berepresented in its protonated form by formula (V′):

wherein each R is defined as above with respect to formula (V).

In one embodiment of the ligand represented by formula (V), R₁, R₄, R₅and R₈ are independently H, methyl or ethyl; R₂ and R₃ together with thenitrogen atom to which they are attached form pyridinyl, and; R₆ and R₇together with the nitrogen atom to which they are attached formpyridinyl. In a specific embodiment of the ligand represented by formula(V), R₁, R₄, R₅ and R₈ are H; R₂ and R₃ together with the nitrogen atomto which they are attached form pyridinyl, and; R₆ and R₇ together withthe nitrogen atom to which they are attached form pyridinyl.

For use in ALD methods, it is desirable to have a high vapor pressureprecursor. With respect to the L-(bisamineazaallylic) metal coordinationcomplexes of the invention, vapor pressure can be optimized by selectionof functional groups (R) that minimize the overall molecular weight ofthe complex. For this reason, in certain specific aspects of theinvention the ligands represented by formula (V) each R is independentlyH, halide, linear or branched C₁₋₆ alkyl, acyl, aldehyde, keto, C₂₋₄alkenyl or is absent thereby forming an adjacent double bond. In afurther specific aspect, each R is independently H or C₁₋₂ alkyl.

Depending on the oxidation state of the selected metal cation, theligand represented by formula (V) may form a 3-coordinated complex withthe metal and one more L_(neutral) or L_(anionic) ligand(s) as definedabove may also coordinate M. In a specific embodiment the anionicligands include Cl, amido or C₁₋₃ alkyl and neutral ligands includecarbonyl or amino. In an alternative specific embodiment, homolepticbis(bisaminoazaallyllic) metal complexes may be formed in which twoligands represented by formula (V) coordinate a single metal cation,forming a 6-coordinated complex. However, it is to be understood that Lmay be an NNN ligand other than one represented by formula (V).

When an L_(anionic)-bisamineazaallylic metal coordination complex or anL_(neutral)-bisamineazaallylic metal coordination complex is used as themetal source material in the thin film deposition processes of theinvention, the bond between the metal and L is reduced by hydrogen atomson the substrate surface, releasing H L_(anionic) or L_(neutral) whichis purged prior to introduction of the reducing gas. The reducing gas,such as hydrogen, reduces the covalent bond between the metal and theazaallyl nitrogen to release the bisamineazallylic (NNN) ligand and formthe first atomic layer of elemental metal on the surface.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It will be apparent to those skilled in the art thatvarious modifications and variations can be made to the method andapparatus of the present invention without departing from the spirit andscope of the invention. Thus, it is intended that the present inventioninclude modifications and variations that are within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A metal complex having a formula

wherein M is a transition metal; each R is independently H, halide,linear or branched C₁₋₆ alkyl, acyl, aldehyde, keto, C₂₋₄ alkenyl, or isabsent thereby forming an adjacent double bond; and L is anM-coordinating ligand selected from the group consisting of neutralligands, anionic ligands and mixed ligands.
 2. The metal complex ofclaim 1, wherein L is a bisamineazaallylic ligand.
 3. The metal complexof claim 2 wherein L has a formula:

or the corresponding protonated form thereof, wherein each R isindependently H, halide, linear or branched C₁₋₆ alkyl, acyl, aldehyde,keto, C₂₋₄ alkenyl, or is absent thereby forming an adjacent doublebond.
 4. The metal complex of claim 1 wherein L is halogen or methyl. 5.The metal complex of claim 1 prepared by a method comprising: a)reacting an aldehyde compound having a formula R₁R₂N—CH₂—COH with acompound having a formula R₃R₄N—CH₂CH₂NH₂ to form a reaction productrepresented by formula R₁R₂N—CH₂—CH═N—CH₂—CH₂—NR₃R₄; b) treating thereaction product with lithium hexamethyldisilazide (LHMDS) to produce aligand coordinated with a lithium ion, and; c) forming the transitionmetal complex by reacting the ligand coordinated with the lithium ionand a transition metal halide.
 6. The metal complex of claim 1, whereinthe neutral ligands include C₁₋₃ alkyll, amido, and imido ligands,anionic ligands include halide ligands, and mixed ligands includeamidinate, amido-amino, and pyrollylamino ligands.